mbed-os/tools/test/config_test/test21/mbed_app.json

{
    "custom_targets": {
        "test_target": {
            "core": "Cortex-M0",
            "extra_labels": [],
            "features": [],
            "default_build": "standard"
        }
    },
    "target_overrides": {
        "*": {
            "target.features": ["IPV4", "IPV6"]
        }
    }
}